In recent years, with the popularization of digital cameras and camcorders, people demand more and more glass lens for major components. In addition, due to pixel increase of imaging device in the digital camera, optical elements like glass lens require higher performance. Since aspheric element could better eliminate the spherical aberration and reduce the number of optical elements, aspheric element hits the mainstream in optical design.
High-precision molding, a commonly used method for aspheric molding, refers to press molding of glass perform under high temperature by mould for female die with predetermined shape, in order to obtain the final shape or glass molded article with shape similar to the final shape. Molded products with desired shape may be efficiently produced by high-precision molding. Besides, the aspheric lenses manufactured with high-precision molding technology usually no longer require grinding and polishing, thereby reducing costs and improving productivity. In order to replicate the high-precision modular surface on the glass moldings during high-precision molding, the glass preform is required to be pressurized under high temperature. At this point, shaping mould is exposed under high temperature with higher pressure. The surface layer of compression mold remains vulnerable to oxidative attack even under protection. If expensive high-precision mould is frequently changed during high-precision molding, low cost and high productivity will not be achieved. To prolong the service life of mould and reduce damage to the shaping mould by high-temperature environment, molding temperature shall be reduced as much as possible. Therefore, optical material developer aims to develop optical glass with transition temperature (Tg) as low as possible.
Cost saving not only can realized by prolonging the service life of shaping mould, but also by reducing raw material costs. CN1182058C discloses a high-refractivity optical glass, in which a large amount of high-cost Ta2O5 is applied, so it is not suitable for large-volume industrial production.